Orbital Parameters of the Binary Companion in o and Using Spectrum Disentangling

o And is one of the most frequently observed Be stars, both in photometry and spectroscopy. It is a multiple system of at least four stars (a Be star, a close binary of spectral types B7 and B8, and an A star). For over a century, numerous observers report a highly variable spectrum, photometric changes, and a substantial range of radial velocity. The star has changed back and forth between a shell-type and a normal B-type star. The last emission phase started in 1992 and ended in 2000. Analysis of the dynamical spectra at spectral lines Mg II 4481 Å and He I 6678 Å and radial velocity curves shows that the two binary components can be resolved. We decomposed the triple star spectra and computed orbital parameters of the binary companion using the KOREL code for spectrum disentangling.     

A spectral differential approach to characterizing low‐mass companions to late‐type stars

In this paper, we develop a spectral differential technique with which the dynamical mass of low‐mass companions can be found. This method aims at discovering close companions to late‐type stars by removing the stellar spectrum through a subtraction of spectra obtained at different orbital phases and discovering the companion spectrum in the difference spectrum in which the companion lines appear twice (positive and negative signal). The resulting radial velocity difference of these two signals provides the true mass of the companion, if the orbital solution for the radial velocities of the primary is known. We select the CO line region in the K band for our study, because it provides a favourable star‐to‐companion brightness ratio for our test case GJ 1046, an M2V dwarf with a low‐mass companion that most likely is a brown dwarf. Furthermore, these lines remain largely unblended in the difference spectrum so that the radial velocity amplitude of the companion can be measured directly. Only if the companion rotates rapidly and has a small radial velocity due to a high mass, does blending occur for all lines so that our approach fails. We also consider activity of the host star, and show that the companion difference flux can be expected to have larger amplitude than the residual signal from the active star so that stellar activity does not inhibit the determination of the companion mass. In addition to determining the companion mass, we restore the single companion spectrum from the difference spectrum using singular value decomposition. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Proper motion and X‐ray selected search for new members of the young TW Hya association

We have searched for new members of the TWHya association (TWA) among unidentified ROSAT X‐ray sources by identifying them in proper motion catalogues and selecting those that would be consistent with kinematical membership to the TWA. Spectroscopic follow‐up observations of 19 member candidates revealed the detection of moderate lithium absorption lines for the following three stars: GSC 7206 845, TYC 7216‐55, and TYC 7247‐12. The isochronal ages of the latter TYC stars are estimated to be ∼20 Myr while the other one has ∼100 Myr age based on a kinematic distance estimate that assumes TWA membership. However, the moderately Li‐rich stars are not likely to be new pre‐main sequence members of TWA partly because of the discrepant radial velocities. Infrared follow‐up imaging in the H‐band for the 3 stars shows companion candidates near two of them.While one system (TYC 7216‐55) is probably a near‐equal‐magnitude stellar binary, our follow‐up H‐band spectrum of the faint companion candidate near GSC 7206 845 shows that it is instead a background K‐type star rather than a companion. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Binarity and multiperiodicity in high-amplitude δ Scuti stars

We have carried out a photometric and spectroscopic survey of bright high-amplitude δ Scuti (HADS) stars. The aim was to detect binarity and multiperiodicity (or both) in order to explore the possibility of combining binary star astrophysics with stellar oscillations. Here, we present the first results for 10, predominantly southern, HADS variables. We detected the orbital motion of RS Gru with a semi-amplitude of ∼6.5 km s⁻¹ and 11.5 d period. The companion is inferred to be a low-mass dwarf star in a close orbit around RS Gru. We found multiperiodicity in RY Lep from both photometric and radial velocity data and detected orbital motion in the radial velocities with hints of a possible period of 500–700 d. The data also revealed that the amplitude of the secondary frequency is variable on the time-scale of a few years, whereas the dominant mode is stable. Radial velocities of AD CMi revealed cycle-to-cycle variations, which might be due to non-radial pulsations. We confirmed the multiperiodic nature of BQ Ind, while we obtained the first radial velocity curves of ZZ Mic and BE Lyn. The radial velocity curve and the O–C diagram of CY Aqr are consistent with the long-period binary hypothesis. We took new time series photometry on XX Cyg, DY Her and DY Peg, with which we updated their O–C diagrams.     

Composite spectra XIX: HD 208253, a long‐period binary whose hot secondary has enhanced strontium and barium

We separate and analyse the component spectra of the composite‐spectrum binary HD 208253. We find that the cool primary is an evolving star of spectral type G7 III, while its hot secondary is an early‐A dwarf. The giant is currently near the lowest point of the red‐giant branch and is slightly less luminous than its dwarf companion. We provide a set of precise radial‐velocity measurements for both stars. The double‐lined orbit which we derive from them shows that the component mass ratio is close to unity (q = 1.05 ± 0.01). We deduce the physical properties of both stars, determine their respective masses to be 2.75 ± 0.07 Me (giant) and 2.62 ± 0.07 Me (dwarf), and show that the orbit's inclination is within a degree or two of 68°. The spectrum of the A‐type component has quite component has quite narrow lines (we infer a rotational velocity of 18 km s^–1), though since the period of the orbit is well over 1 year that component cannot be in synchronous rotation. An intriguing property of the dwarf is its enhanced Sr and Ba, though it does not exhibit the other spectral peculiarities that would signal a classical Am star. While by no means unique amongst the multitude of oddities exhibited by A and early‐F stars, this dwarf which we have uncovered in a long‐period binary offers valuable constraints and challenges to stellar‐evolution theory. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Analysis of fundamental parameters for V477 Lyr

We analyze the photometric and spectroscopic observations of the young pre-cataclysmic variable (pre-CV) V477 Lyr. The masses of both binary components have been corrected by analyzing their radial velocity curves. We show that agreement between the theoretical and observed light curves of the object is possible for several sets of its physical parameters corresponding to the chosen temperature of the primary component. The final parameters of V477 Lyr have been established by comparing observational data with evolutionary tracks for planetary nebula nuclei. The derived effective temperature of the O subdwarf is higher than that estimated by analyzing the object’s ultraviolet spectra by more than 10000 K. This is in agreement with the analogous results obtained previously for the young pre-CVs V664 Cas and UU Sge. The secondary component of V477 Lyr has been proven to have a more than 25-fold luminosity excess compared to main-sequence stars of similar mass. Comparison of the physical parameters for the cool stars in young pre-CVs indicates that their luminosities do not correlate with the masses of the objects. The observed luminosity excesses in such stars show a close correlation with the post-common-envelope lifetime of the systems and should be investigated within the framework of the theory of their relaxation to the state of main-sequence stars.     

Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system

The Pulkovo Compilation of Radial Velocities (PCRV) has been made to study the stellar kinematics in the local spiral arm. The PCRV contains weighted mean absolute radial velocities for 35 495 Hipparcos stars of various spectral types and luminosity classes over the entire celestial sphere mainly within 500 pc of the Sun. The median accuracy of the radial velocities obtained is 0.7 km s^?1. Results from 203 publications were used in the catalogue. Four of them were used to improve the radial velocities of standard stars from the IAU list. The radial velocities of 155 standard stars turned out to be constant within 0.3 km s^?1. These stars were used to analyze 47 768 mean radial velocities for 37 200 stars from 12 major publications (～80% of all the data used). Zero-point discrepancies and systematic dependences on radial velocity, B-V color index, right ascension, and declination were found in radial velocity differences of the form “publication minus IAU list of standards.” These discrepancies and dependences were approximated and taken into account when calculating the weighted mean radial velocities. 1128 stars whose independent radial-velocity determinations were available at least in three of these publications and agreed within 3 km s^?1 were chosen as the work list of secondary standards. Radial-velocity differences of the form “publication minus list of secondary standards” were used by analogy to correct the zero points and systematic dependences in the radial velocities from 33 more publications (～ 13% of the data used). In addition, the radial velocities from 154 minor publications (～7% of the data used) pertaining to well-known instruments were used without any corrections.     

The orbit of the visual binary ADS 8630 (γ Vir)

We present a new orbit for the visual binary ADS 8630 = γ Vir. Although it is one of the first visual double stars discovered, its orbital elements were still poorly known. Indeed the very high eccentricity of the orbit and the difficulty of observing the pair at periastron passage in 1836 has meant that it is only now that sufficient measures of the recent close approach in 2005 have allowed an orbital analysis which predicts the angular motion to an acceptable degree of accuracy. We present a series of 35 speckle measurements of ADS 8630 obtained with PISCO in Merate between 2004 and 2006. Those measures have been crucial for determining the new orbital elements since they cover an arc of 130 degrees in the apparent orbit and include the periastron passage of 2005. The masses of the individual F0V components of the binary are found to be 1.40 M_⊙ with an accuracy of about 3%. We also investigate in detail the possibility of the presence of a third body in the system, that was proposed by other authors. The high‐angular resolution infra‐red image of γ Vir that we obtained in June 2006 with the LuckyCam instrument on the ESO NTT shows the absence of any companion as faint as a M0V star at a distance larger than 0.4″. Combined with the analysis of the residuals of our orbit, the values found for the masses of the individual components and the radial velocity measurements, this observation rules out the presence in the system of a third companion with a mass larger than 0.3 M_⊙. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Composite spectra

Composite-spectrum binary stars generally consist of a late-type giant and a main-sequence star of type A or B. Their spectra are therefore rather confusing; but by a technique of digital subtraction of the spectra of appropriate single late-type giants, composite spectra can be split into their individual components. In favourable cases the radial velocities of both components can be measured and the mass ratio determined. The procedures are illustrated by reference to HR 6902, a fifth-magnitude composite-spectrum binary. Its components are shown to have spectral types of G9 II and B8 V, with a mass ratio of 1.31, and its orbit is determined. There is some evidence that the system shows eclipses. If it does, the masses of the components are 3.9 and 3.0M⊙ respectively, and HR 6902 becomes the sixth known member of the important class ofζ Aur binaries.     

“Constant” eclipsing binary in the instability strip

The eclipsing binary OO Peg consist of two late-A type stars in circular orbit with a period of 2.985 days. I use the high-resolution spectroscopic and extensive light curves from the ASAS and Hipparcos survey to measure the physical properties of the system. Previous attempts to model the light and radial velocity curves of the system have met with limited success, primarily because of the lack of a accurate photometric data. The system shows no signs of stellar activity, it is slowly rotating, has not been detected period changes, and there is no pulsational signs in the photometric data. I show the location of the components in effective temperature vs. luminosity diagram compared to the instability region limits established from eclipsing binary components. While more than 25 system have been plotted to diagram, about six single stars and OO Peg components do not show any pulsational frequencies. They are apparently constant stars lie within the pulsation instability region. I speculate as to the possible causes of this picture.     

The stellar mass ratio of GK Persei

We study the absorption lines present in the spectra of the long-period cataclysmic variable GK Per during its quiescent state, which are associated with the secondary star. By comparing quiescent data with outburst spectra we infer that the donor star appears identical during the two states and the inner face of the secondary star is not noticeably irradiated by flux from the accreting regions. We obtain new values for the radial velocity semi-amplitude of the secondary star,     , a projected rotational velocity,     and consequently a measurement of the stellar mass ratio of GK Per,     . The inferred white dwarf radial velocities are greater than those measured traditionally using the wings of Doppler-broadened emission lines suspected to originate in an accretion disc, highlighting the unsuitability of emission lines for mass determinations in cataclysmic variables. We determine mass limits for both components in the binary,     and     .     

TRIMOR – three-dimensional correlation technique to analyse multi-order spectra of triple stellar systems: application to HD 188753

This paper presents a new algorithm, trimor , to analyse multi-order spectra of triple systems. The algorithm is an extension of tricor , the three-dimensional correlation technique that derives the radial velocities of triple stellar systems from single-order spectra. The combined correlation derived from many orders enables the detection and the measurement of radial velocities of faint tertiary companions. The paper applied trimor to the already available spectra of HD 188753, a well-known triple system, yielding the radial velocities of the faintest star in the system. This rendered the close pair of the triple system a double-lined spectroscopic binary, which led to a precise mass ratio and an estimate of its inclination. The close-pair inclination is very close to the inclination of the wide orbit, consistent with the assertion that this triple system has a close to coplanar configuration.     

Seismic signatures of strange stars with crust

We study acoustic oscillations (eigenfrequencies, velocity distributions, damping times) of normal crusts of strange stars. These oscillations are very specific because of huge density jump at the interface between the normal crust and the strange matter core. The oscillation problem is shown to be self-similar. For a low (but non-zero) multipolarity l , the fundamental mode (without radial nodes) has a frequency of ∼300 Hz and mostly horizontal oscillation velocity; other pressure modes have frequencies ≳20 kHz and almost radial oscillation velocities. The latter modes are similar to radial oscillations (having approximately the same frequencies and radial velocity profiles). The oscillation spectrum of strange stars with crust differs from the spectrum of neutron stars. If detected, acoustic oscillations would allow one to discriminate between strange stars with crust and neutron stars and constrain the mass and radius of the star.     

Another channel to detect close-in binary companions via gravitational microlensing

Gaudi & Gould showed that close companions of remote binary systems can be efficiently detected by using gravitational microlensing via the deviations in the lensing light curves induced by the existence of the lens companions. In this paper, we introduce another channel to detect faint close-in binary companions by using microlensing. This method utilizes a caustic-crossing binary lens event with a source also composed of binary stars, where the companion is a faint star. Detection of the companion is possible because the flux of the companion can be highly amplified when it crosses the lens caustic. The detection is facilitated since the companion is more amplified than the primary because it, in general, has a smaller size than the primary, and thus experiences less finite source effect. The method is an extension of the previous one suggested to detect close-in giant planets by Graff & Gaudi and Lewis & Ibata and further developed by Ashton & Lewis. From the simulations of realistic Galactic bulge events, we find that companions of K-type main-sequence or brighter stars can be efficiently detected from the current type of microlensing follow-up observations by using the proposed method. We also find that compared with the method of detecting lens companions for which the efficiency drops significantly for binaries with separations ≲0.2 of the angular Einstein ring radius, θ _E, the proposed method has an important advantage of being able to detect companions with substantially smaller separations down to ∼     .     

HS 2333 + 3927: a new sdB binary with a large reflection effect

We report the discovery of a binary, HS 2233 + 3927, consisting of an sdB star with a faint companion. From its lightcurve the orbital period of 14,844 s, the mass ratio, the inclination, and other system parameters are derived. The companion does not contribute to the optical light of the system except through a strong reflection effect. The semi-amplitude of the radial velocity curve K ₁= 89.6 km/s^?1 and a mass function of f(m) = 0.013 M _⊙ are determined. A preliminary spectroscopic analysis of the blue spectra using NLTE model atmospheres results in T_eff= 36 500 K, log g= 5.70, and log(n _He/n _H) =?2.15. These parameters are typical for sdB stars, the companion is probably an M dwarf.     

Analysis of the optical emission of the young precataclysmic variables HS 1857+5144 and ABELL 65

We analyze the physical state and the properties of the close binary systems HS 1857+5144 and Abell 65. We took the spectra of both systems over a wide range of orbital phases with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) and obtained their multicolor light curves with the RTT150 and Zeiss-1000 telescopes of the SAO RAS. We demonstrate that both Abell 65 and HS 1857+5144 are young precataclysmic variables (PV) with orbital periods of P _orb = 1. ^d 003729 and P _orb = 0. ^d 26633331, respectively. The observed brightness and spectral variations during the orbital period are due to the radiation of the cold component, which absorbs the short-wave radiation of the hot component and reemits it in the visual part of the spectrum. A joint analysis of the brightness and radial velocity curves allowed us to find the possible and optimum sets of their fundamental parameters. We found the luminosity excesses of the secondary components of HS 1857+5144 and Abell 65 with respect to the corresponding Main Sequence stars to be typical for such objects. The excess luminosities of the secondary components of all young PVs are indicative of their faster relaxation rate towards the quiescent state compared to the rates estimated in earlier studies.     

The effects of mutual irradiation on the observed radial velocity of the components of close binary systems

The aim of the present paper will be to investigate the effects, on the observed radial velocities of the components of close binary systems, of atmospheric motions caused by mutual irradiation of the two stars. Such motions can (and, in general, will) produce systematic differences between the observed radial velocity and that of the centre of mass of the respective star — differences varying with with the phase and thus giving rise to spurious deformations of the star's radial-velocity curves due to orbital motion. A failure to separate the two could (and in general, will) vitiate the physical elements deduced from these curves —such as the masses or absolute dimensions of the components and of the shape of their orbit; but in order to do so, an investigation of atmospheric motions invoked by irradiation becomes a necessary prerequisite.In the Introduction following this abstract, the problem at issue will be described in general terms, and phenomena outlined which should arise in this connection (together with the observations indicating their presence). In Section 2, general expressions for the radial velocity at any point of stellar surface arising from atmospheric motions will be formulated while Section 3 will isolate such velocities for components of close binary systems as are produced by mutual irradiation of their mates, in terms of hydrodynamical equations of radiative transfer describing the problem. In Sections 4 and 5, the effects of non-rotational motions on the observed radial velocities will be specified, and hydrodynamical equations formulated which specify atmospheric convection caused by irradiation of each component of a close binary by its mate. Linearized versions of such equations will be constructed in Section 6; while Section 7 contains an evaluation of the effects which such gas streams exert on the observed radial velocity of the stars.In the concluding Section 8 applications to practical cases are carried out. It will be shown that no reliable spectroscopic elements of close binary systems (including the masses and absolute dimensions of their components) can be obtained until the effects of atmospheric convection caused by mutual irradiation have been accounted for to permit us to convert the observed radial velocities (influenced as they are by the motion of as in which they originate) to those of the centre of mass of the respective stars.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988.     

A runaway binary star escaping from the Θ<Superscript>1</Superscript> ori system

A runaway binary star escaping in runaway from the multiple system Θ¹ Ori C is studied. The radial velocities of both components are measured and radial velocity curves are constructed and solved for them. The physical parameters and chemical compositions of the stars are determined.     

Detection of the spectroscopic binary (SB2) nature of BD-6°1178 = IRAS 05238-0626

The star BD-6°1178, which is identified with the IRAS 05238-0626 source, is shown for the first time to be a spectroscopic binary (SB2) by analyzing the high-resolution spectra taken with the NES echelle spectrograph of the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. The components of the binary have close spectral types and luminosity classes: F5 IV–III and F3V. The heliocentric radial velocities are measured for both components at four time moments in 2004–2005. The two stars have close rotation velocities, which are equal to 24 and 19 km/s. We do not confirm the classification of BD-6°1178 as a supergiant in the state of becoming a planetary nebula. BD-6°1178 probably is a young pre-MS stars. It is possibly a member of the 1c subgroup of the OriOB1 association.     

The first high-precision radial velocity search for extra-solar planets

The reflex motion of a star induced by a planetary companion is too small to detect by photographic astrometry. The apparent discovery in the 1960s of planetary systems around certain nearby stars, in particular Barnard’s star, turned out to be spurious. Conventional stellar radial velocities determined from photographic spectra at that time were also too inaccurate to detect the expected reflex velocity changes. In the late 1970s and early 1980s, the introduction of solid-state, signal-generating detectors and absorption cells to impose wavelength fiducials directly on the starlight, reduced radial velocity errors to the point where such a search became feasible. Beginning in 1980, our team from UBC introduced an absorption cell of hydrogen fluoride gas in front of the CFHT coudé spectrograph and, for 12 years, monitored the radial velocities of some 29 solar-type stars. Since it was assumed that extra-solar planets would most likely resemble Jupiter in mass and orbit, we were awarded only three or four two-night observing runs each year. Our survey highlighted three potential planet hosting stars, γ Cep (K1 IV), β Gem (K0 III), and ? Eri (K2 V). The putative planets all resembled Jovian systems with periods and masses of: 2.5 years and 1.4 M_J, 1.6 years and 2.6 M_J, and 6.9 years and 0.9 M_J, respectively. All three were subsequently confirmed from more extensive data by the Texas group led by Cochran and Hatzes who also derived the currently accepted orbital elements.None of these three systems is simple. All five giant stars and the supergiant in our survey proved to be intrinsic velocity variables. When we first drew attention to a possible planetary companion to γ Cep in 1988 it was classified as a giant, and there was the possibility that its radial velocity variations and those of β Gem (K0 III) were intrinsic to the stars. A further complication for γ Cep was the presence of an unseen secondary star in an orbit with a period initially estimated at some 30 years. The implication was that the planetary orbit might not be stable, and a Jovian planet surviving so close to a giant then seemed improbable. Later observations by others showed the stellar binary period was closer to 67 years, the primary was only a sub-giant and a weak, apparently synchronous chromospheric variation disappeared. Chromospheric activity was considered important because κ¹ Cet, one of our program stars, showed a significant correlation of its radial velocity curve with chromospheric activity.? Eri is a young, magnetically active star with spots making it a noisy target for radial velocities. While the signature of a highly elliptical orbit (e = 0.6) has persisted for more than three planetary orbits, some feel that even more extensive coverage is needed to confirm the identification despite an apparent complementary astrometric acceleration detected with the Hubble Space Telescope.We confined our initial analyses of the program stars to looking for circular orbits. In retrospect, it appears that some 10% of our sample did in fact have Jovian planetary companions in orbits with periods of years.